Surgical instrument and system

ABSTRACT

An electrosurgical system includes an electrosurgical unit electrically coupled to a surgical retractor. The electrosurgical unit includes an RF output and an RF return. The surgical retractor includes a return pad electrically coupled to the RF return of the electrosurgical unit. The electrosurgical unit includes an RF output configured to be coupled to an electrosurgical device, such as an electrosurgical device configured in a monopolar mode. A controller is configured to determine an impedance in tissue at a surgical area electrically disposed between the RF output and the and the RF return. The surgical retractor includes a handle and a blade configured to interface with tissue. The blade includes a return electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/053,917, filed Aug. 3, 2018, which claims the benefit of U.S.Provisional Application No. 62/549,560, filed Aug. 24, 2017, titled“SURGICAL INSTRUMENT AND SYSTEM,” the disclosures of which areincorporated herein by reference.

BACKGROUND

This disclosure relates generally to the field of medical devices,systems and methods for use in surgical procedures. More specifically,this disclosure relates to surgical instruments to manipulate tissue,such as surgical retractors or expanders. In one example, the surgicalinstruments can be used with electrosurgical devices, units, systems ormethods that can provide for cutting, coagulation, hemostasis, orsealing of bodily tissues with an electrosurgical device.

Surgical instruments such as surgical retractors and expanders are usedto manipulate tissues including skin, muscles, bone, and organs of apatient and are commonly used in surgery by clinicians. For example,such surgical instruments can separate tissues either at the edges of asurgical incision or wound or can hold back tissues to facilitate theaccess of tissues under the incision such as to create more room for aclinician to view or to insert other surgical instruments, includingelectrosurgical devices, into a surgical cavity. Under one distinction,surgical retractors tend to pull the tissue while extractors perform asimilar function but tend to push the tissue. For the purposes of thisdisclosure, such surgical instruments are both generally referred to assurgical retractors.

Working through small incisions, especially in relatively deep surgicalpockets, can present many challenges for clinicians such as surgeons.Surgical instruments including electrosurgical devices and surgicalretractors are often used in this environment, such as in breast andabdominal surgery. While the surgical instruments, including theelectrosurgical devices and surgical retractors are suitable for use invariety of procedures, the examples below may be described withreference to general, plastic, and reconstructive procedures in breastsurgery but are not intended to be limited to such procedures.

One example surgical procedure in which electrosurgical devices andsurgical retractors are often used includes skin sparing mastectomiesand nipple sparing mastectomies. Surgical management of breast cancerhas evolved since the radical mastectomy, or Halsted mastectomy.Clinicians have sought procedures to improve oncologic outcomes andcombine the techniques of plastic surgery to maximize both cancertreatment and aesthetic effect since the introduction of a skin sparingmastectomy. In a skin sparing mastectomy, all breast tissue and thenipple are removed, but more of the native breast skin is preserved thanin a radical mastectomy. The skin sparing mastectomy provides a moreenhanced cosmetic result in patients undergoing immediate reconstructionthan the radical mastectomy. Although some may consider a skin sparingmastectomy with immediate breast reconstruction the current standard ofpractice, nipple sparing mastectomy is an advanced surgical option forthe treatment of breast cancer is rapidly becoming the preferredsurgical option in many patients. The nipple sparing mastectomy providesan effective oncologic surgical outcome and preserves the skin and thenipple-areola complex for improved aesthetics.

Historically, the technique of preserving the nipple-areola complexduring mastectomy for breast cancer has been controversial as many feltthat this would lead to an unacceptably high rate of breast cancerrecurrence. Recent advances in the techniques of preserving thenipple-areola complex during risk-reduction prophylactic mastectomy in alarge series of high-risk patients has been described with excellentresults in terms of preventing breast cancer. Low local cancerrecurrence rates following a nipple sparing mastectomy withoutirradiation has further supported the adoption of this approach.

As breast surgeons continue to base their interventions on patientsafety and oncologic efficacy, the advanced technique of a nipplesparing mastectomy has enabled cosmesis to become a significant goal inbreast cancer treatment. Accordingly, patients have increased theirinterest and demand for nipple sparing mastectomies. For example,genetic testing for breast cancer risk assessment has contributed to theincreased the number of nipple sparing mastectomies being performed.

Clinicians seek to improve the techniques used in nipple sparingmastectomies. The type and location of incision used in nipple sparingmastectomy is selected to provide removal of breast tissue, as well asaccess to the axilla for staging in patients with breast cancer. Duringthe nipple sparing mastectomy, the surgeon has the ability to gainaccess to tissue from the base of the nipple for assessment of occultcancer. Inframammary incisions and lateral radial incisions areincreasingly being utilized during the procedure. Both incisions allowcomplete removal of the breast tissue, access to the axilla for staging,and ease of obtaining specimens from the base of the nipple. Inappropriate patients, the inframammary incision, which is similar to theincision used for breast augmentation, is increasingly becoming thepreferred incision location by patients, breast surgeons, and plasticsurgeons for improved aesthetic outcomes.

The growing adoption of nipple sparing mastectomy as a surgical optionfor selected patients has also demonstrated the current surgicallimitations of the nipple sparing mastectomy procedure. Some of theselimitations include limited incision location options, limitedvisualization and access through smaller incisions, access to thesuperior and superior medial aspect of the breast, and the inability orconcern in the ability to maintain consistent flap thickness andviability.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription.

The viability of breast flap tissue, for example, can be difficult todetect. This disclosure relates to electrosurgical systems, instruments,and methods to monitor electrical characteristics in tissue at thesurgical site, such as during monopolar activation, to monitorconditions in the tissue. For example, rather than rely solely on theelectrical characteristics between monopolar device and return pad, thisdisclosure sets for electrosurgical systems, instruments, and methods ofmonitoring the signals, such as current, through a monopolar ormulti-polar electrosurgical return electrode in a surgical retractor toincrease awareness of tissue viability. In one example, anelectrosurgical unit can analyze the electrical characteristics receivedin the surgical retractor at the surgical site to determine changes overtime, such as a loss of conductivity of the tissue adjacent to thesurgical retractor. For instance, rather than measuring the thermaleffects at the site of the electrosurgical device, the systems,instruments, and method provide a return path through the tissue nearthe surgical retractor and analyze the signal for any loss ofconductivity over time.

In one aspect, the disclosure relates to an electrosurgical systemhaving an electrosurgical unit electrically coupled to a surgicalretractor. The electrosurgical unit includes an RF output and an RFreturn. The surgical retractor includes a return pad electricallycoupled to the RF return of the electrosurgical unit.

In another aspect, the disclosure relates to an example of anelectrosurgical unit. The electrosurgical unit includes an RF outputconfigured to be coupled to an electrosurgical device, such as anelectrosurgical device configured in a monopolar mode, and an RF returnconfigured to be coupled to a surgical retractor. The electrosurgicalunit also includes a controller operably coupled to the RF output andthe RF return. The controller is configured to determine an impedance intissue at a surgical area electrically disposed between the RF outputand the and the RF return.

In still another aspect, the disclosure relates to another example of anelectrosurgical unit. The electrosurgical unit includes an RF outputconfigured to be coupled to an electrosurgical device, a first RF returnconfigured to be coupled to one of the electrosurgical device and areturn pad dispersive electrode, and a second RF return configured to becoupled to a surgical retractor. The electrosurgical unit includes acontroller configured to determine an impedance in tissue at a surgicalarea electrically disposed between the RF output and the second RFreturn. The controller is also configured to determine an impedance intissue at a surgical area electrically disposed between the RF outputand the and the first RF return.

In still another aspect, the disclosure relates to a surgical retractorhaving a handle and a blade configured to interface with tissue. Theblade includes a return electrode.

In still another aspect, the disclosure relates to a blade for asurgical retractor, the blade includes an non-conductive base portionhaving a major surface and a return electrode disposed on the majorsurface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view illustrating an embodiment of a system accordingto the present disclosure including an example electrosurgical unit incombination with an example handheld electrosurgical device and anexample surgical retractor.

FIG. 2 is a schematic view illustrating the example electrosurgical unitin combination with the example handheld electrosurgical device and theexample surgical retractor in the system of FIG. 1 .

FIG. 3 is a schematic view illustrating another example electrosurgicalunit in combination with the example handheld electrosurgical device, anexample patient return pad, and the example surgical retractor of FIG. 2.

FIG. 4 is a perspective view illustrating an example surgical retractorsuitable for use in the system of FIG. 1 .

FIG. 5 is a perspective view illustrating another example surgicalretractor suitable for use in the system of FIG. 1 .

DETAILED DESCRIPTION

Throughout the description, like reference numerals and letters indicatecorresponding structure throughout the several views. Also, anyparticular features(s) of a particular exemplary embodiment may beequally applied to any other exemplary embodiment(s) of thisspecification as suitable. That is, features between the variousexemplary embodiments described herein are interchangeable as suitableand may not be exclusive. From the specification, it should be clearthat the terms “distal” and “proximal” are made in reference to a userof the device.

Electrosurgery includes such techniques as cutting, coagulation,hemostasis, or sealing of tissues with the aid of electrodes energizedwith a suitable power source. Typical electrosurgical devices apply anelectrical potential difference or signal between an active electrodeand a return electrode on a patient's grounded body in a monopolararrangement or between an active electrode and a return electrode on thedevice in bipolar arrangement to deliver electrical energy to the areawhere tissue is to be affected. The electrosurgical devices aretypically held by a clinician, such as surgeon, and connected to thepower source, such as an electrosurgical unit having a power generator,via cabling.

Electrosurgical devices pass electrical energy through tissue betweenthe electrodes to provide coagulation to control bleeding and hemostasisto seal tissue. Electrosurgical devices can also cut tissue through theuse of plasma formed on the electrode. Tissue that contacts the plasmaexperiences a rapid vaporization of cellular fluid to produce a cuttingeffect. Typically, cutting and coagulation are often performed withelectrodes in the monopolar arrangement while hemostasis is performedwith electrodes in the bipolar arrangement.

Electrical signals can be applied to the electrodes either as a train ofhigh frequency pulses or as a continuous signal typically in theradiofrequency (RF) range to perform the different techniques. Thesignals can include a variable set of parameters, such as power orvoltage level, waveform parameters such as frequency, pulse duration,duty cycle, and other signal parameters that may be particularly apt orpreferred for a given technique. For example, the clinician could cuttissue using a first RF signal having a set of parameters to form plasmaand control bleeding using a second RF signal having another set ofparameters more preferred for coagulation. The clinician could also useelectrodes in a bipolar arrangement or a bipolar electrosurgical devicefor hemostatic sealing of the tissue that would employ additional RFsignals having another set of parameters.

In some examples, two distinct electrosurgical devices, one monopolarand the other bipolar, are used to perform different functions insurgery, such as tissue cutting and coagulating and tissue sealing. Forexample the clinician could use a monopolar electrosurgical device tocut and coagulate tissue and use a bipolar electrosurgical device toseal the tissue. In another example, some electrosurgical devices arecapable of performing multiple techniques such as cutting andcoagulating tissue or cutting, coagulating, and sealing tissue,including fluid-assisted sealing of tissue. Several such electrosurgicaldevice are described, for example, in U.S. Pat. No. 8,632,533 toGreeley, et al., U.S. Patent Application Publication No. 2012/000465 toConley, et al., U.S. Patent Application Publication No. 2011/0178515 toBloom et al., U.S. Patent Application Publication No. 2016/0045250 toSylvester, et al., U.S. Patent Application Publication No. 2017/0172646to Patel, et al., U.S. Patent Application Publication No. 2017/0056099to Hubelbank, et al., each assigned to the assignee of the presentdisclosure and incorporated by reference herein in their entireties tothe extent they are not inconsistent with the present disclosure.

In some examples, several such multifunction electrosurgical devicesthat have been developed include a hand piece having two electrodes thatare capable of selectively operating in a monopolar mode and a bipolarmode. These devices can be configured as bipolar electrodes connected toa source of bipolar power to operate in a bipolar mode, for example toseal tissue. To operate the same two-electrode device in a monopolarmode, for example to cut tissue, one of the two electrodes may beselectively deactivated and the other of the two electrodes coupled to asource of monopolar power. In this manner, the multifunction device mayprovide treatment to tissue utilizing one or both electrodes dependingupon the desired tissue treatment.

In other examples, a multifunction surgical device can be configuredusing a plurality of monopolar electrodes that are separately activatedand each operated in a monopolar mode. For example, a first monopolarelectrode configured as a monopolar blade can be specificallyconstructed for cutting or desiccating tissue and operated with cuttingand coagulating RF energy, which is performed with a relatively highimpedance electrode and a high current density to form plasma. A secondmonopolar electrode can be specifically configured to perform thetechniques of hemostatic tissue sealing, which is performed with arelatively lower impedance electrode and a lower current density and adispersed fluid.

Electrosurgical devices can be operated with electrosurgical units thatcan include monopolar and bipolar outputs and detect which activationswitch on the device is selected. One such electrosurgical unit isavailable under the trade designation AEx from Medtronic Advanced Energyof Portsmouth, New Hampshire. The electrosurgical unit, in one example,uses a topology of circuit elements, such as a resistor ladder or othercircuit configuration, to determine which activation switch of aconnected electrosurgical device is selected. In the example, theelectrosurgical unit can provide RF signals corresponding with at leastthree electrosurgical functions such as hemostatic sealing in bipolarconfiguration, cutting in monopolar configuration, and coagulation inmonopolar configuration.

FIG. 1 illustrates a front view of one example of a system 50 thatincludes an electrosurgical unit 10 in combination with an examplehandheld electrosurgical device 30 and a surgical retractor 40. Theelectrosurgical unit 10 provides RF energy to an active electrode on theelectrosurgical device 30 to be applied to tissue of a patient andreceives a return signal via the surgical retractor 40 in contact withthe patient. The electrosurgical unit 10 is able to detect electricalcharacteristics (impedance, components of impedance such as resistanceor reactance, or their changes) of the signal passing through thepatient between the electrosurgical device 30 and the surgical retractor40 to provide information regarding the viability of the tissue adjacentto the surgical retractor 40.

The electrosurgical device 30, in one example, can be a single modeelectrosurgical device such as a monopolar device, which may beconfigured to provide at least one or more of cutting and sealingincluding electrocautery and coagulation, or a bipolar device, which maybe configured to provide hemostatic sealing of tissue in combinationwith a fluid source 20. In another example, the electrosurgical device30 can be a multifunction electrosurgical device configurable for use incutting and sealing including electrocautery and coagulation in a firstmode, such as a monopolar mode or a first monopolar mode, and can beconfigured to provide for hemostatic sealing of tissue in combinationwith a fluid source 20 in a second mode, such as a bipolar mode or asecond monopolar mode, or for other electrical surgical procedures. Instill another example, the electrosurgical device 30 can be configuredfor use in an electrical stimulation mode that may not include cutting,coagulating, or hemostasis.

The surgical retractor 40 can include a conductive return pad configuredto interface with tissue on the patient. The return pad on the surgicalretractor 40 may be disposed on any surface of the surgical retractor 40and will provide a return signal from the electrosurgical device 30 tothe electrosurgical surgical unit 10. In one example, the surgicalretractor 40 may include a blade having a first side configured tointerface with the patient, and the return pad is disposed on the firstside. The return pad on the surgical retractor 40 is also electricallycoupled to the electrosurgical unit 10.

The surgical retractor 40 may be configured in many shapes, sizes, andstyles. For example, the general surgical retractor 40 can include acurved, hooked, or angled blade, or paddle, coupled to a handle that,when held in place, can maintain a desired position of tissue. The blademay include a major surface and a smooth edges or a toothed edge tointerface with tissue and may be coupled to a light source to illuminatethe surgical cavity. The surgical retractor 40 may be part of a kit ofseveral different surgical retractors that are selected to be used in aparticular surgery, or a handle may be selectively coupled to one ofseveral blades. The surgical retractor 40 may single use or reusable.The surgical retractor 40 may be handheld, clamped in situ, or connectedto robotic arms. In still additional examples, the surgical retractor 40can be self-retaining and not need to held once inserted by having twoor more blades that are mechanically separated, such as via spring,ratchet, worm gear, or other mechanism to pull on multiple sides of asurgical cavity, such as rib spreaders or thoracic retractors. Otherconfigurations of the surgical retractor 40 are contemplated.

The system 50 can be carried on a movable cart 2 having a support member4 comprising a hollow cylindrical post which includes a platform 6comprising a pedestal table to provide a flat, stable surface forlocation of the electrosurgical unit 10. Cart 2 can include a pole 8having a height that can be adjusted by sliding the pole 8 up and down.Fluid source 20 can be supported at the top of pole 8.

Fluid source 20 may comprise a bag of fluid from which fluid 12 may flowthrough a drip chamber 14, to delivery tubing 16 and to handheldelectrosurgical device 30. In one example, the fluid 12 includes salineand can include physiologic saline such as sodium chloride (NaCl) 0.9%weight/volume solution. Saline is an electrically conductive fluid, andother suitable electrically conductive fluids can be used. In otherexamples, the fluid may include a nonconductive fluid, such as deionizedwater, which may still provide advantages over using no fluid and maysupport cooling of portions of electrosurgical device 30 and tissue orreducing the occurrence of tissue sticking to the electrosurgical device30.

The fluid delivery tubing 16 in the example passes through pump 22 toconvey fluid to the electrosurgical device 30 and control fluid flow.Pump 22 in one example is a peristaltic pump such as a rotaryperistaltic pump or a linear peristaltic pump. A peristaltic pump canconvey the fluid through the delivery tubing 16 by way of intermittentforces placed on the external surface of the delivery tubing.Peristaltic pumps are often applied during use of the electrosurgicaldevice 30 because the mechanical elements of the pump places forces onthe external surface of the delivery tubing and do not come into directcontact with the fluid, which can reduce the likelihood of fluidcontamination. Other examples of system 60 might not include a pump, andfluid can be is provided to the electrosurgical device 30 via gravity.

The example electrosurgical unit 10 is configured to provide bothmonopolar and bipolar RF power outputs to a specified electrosurgicalinstrument such as electrosurgical device 30. In one example, theelectrosurgical unit 10 can be used for delivery of RF energy toinstruments indicated for cutting and coagulation of soft tissue and fordelivery of RF energy concurrent with fluid to instruments indicated forhemostatic sealing and coagulation of tissue. In one example, theelectrosurgical unit 10 is capable of simultaneously powering specifiedmonopolar and bipolar electrosurgical instruments but may include a lockout feature preventing both monopolar and bipolar output from beingsimultaneously activated.

During monopolar operation of electrosurgical device 30, a firstelectrosurgical electrode, often referred to as an active electrode, isprovided with electrosurgical device 30 while an indifferent, orneutral, electrode is provided in the form of a return pad dispersiveelectrode 42 located on a patient. For example, the return paddispersive electrode 42 is typically on the back, buttocks, upper leg,or other suitable anatomical location during surgery. In such aconfiguration, the return pad dispersive electrode 42 is often referredto as a patient return electrode. An electrical circuit of RF energy isformed between the active electrode and the return pad dispersiveelectrode 42 through the patient. In some examples, the surgicalretractor 40 can be used instead of or in addition to the return paddispersive electrode 42 to detect electrical characteristics of thetissues adjacent to the surgical retractor 40. An electrical circuit ofRF energy is formed between the active electrode and the surgicalretractor 40, such as the return pad on the surgical retractor 40,through the tissue between the active electrode and the surgicalretractor 40.

During bipolar operation of electrosurgical device 30, a secondelectrode, often referred to as the return electrode providing a secondelectrical pole, is provided as part of the device 30. The return paddispersive electrode 42 is typically not used. An electrical circuit ofRF energy is created between the first and second poles of the device30. The current no longer flows through the patient's body to the groundpad dispersive electrode, but rather through a localized portion oftissue between the poles of the device 30. In some examples, thesurgical retractor 40 can be used to provide an additional return pathfor the electrical signals to detect electrical characteristics of thetissues adjacent to the surgical retractor 40.

The electrosurgical device 30 in the example is connected toelectrosurgical unit 10 via cable 24 having plug 25. The electrosurgicalunit 10 can include one or more outputs 26 including a monopolar modeoutput, a bipolar output, or a combination monopolar and bipolar output,which can receive plug 25 and be electrically coupled to the activeelectrode of the electrosurgical device 30 via cable 24. In someexamples, delivery tubing 16 and cable 24 are combined to form a singlecable 26. The electrosurgical unit 10 can also include one or morereturn receptacles 28 that can be electrically coupled to the surgicalretractor 40 and also to the return pad dispersive electrode 42. A cable32 is connected to the surgical retractor 40 and includes plug 33. Plug33 can be mechanically coupled to the electrosurgical device 10 andelectrically connect the return electrode receptacle 28 to the surgicalretractor 40. An additional cable 34 is connected to the return paddispersive electrode 42 and includes plug 35. Plug 35 can bemechanically coupled to the electrosurgical device 10 and electricallyconnect the return electrode receptacle 28 to the return pad dispersiveelectrode 42.

In one example, both the surgical retractor 40 and the return paddispersive electrode 42 are electrically coupled to electrosurgical unitduring surgery to detect the impedance of at least the tissue betweenthe active electrode and the surgical retractor 40. In another example,aspects of the surgery may be performed with the surgical retractor 40disconnected from the electrosurgical unit. In such an example, asurgeon may selectively couple the surgical retractor 40 to theelectrosurgical to monitor impedance in the tissue at the surgical sitebetween the active electrode and the surgical retractor 40 in thepatient at selected times. A clinician may, in one example, decouple thereturn pad dispersive electrode 42, or other return conductor, from theelectrosurgical unit, and electrically couple the surgical retractor 40in its place.

The features of electrosurgical unit 10 described are for illustration,and the electrosurgical units suitable for use with electrosurgicaldevice 30 and surgical retractor may include some, all, or otherfeatures than those described below. In one example, the electrosurgicalunit 10 is capable of operating in at least bipolar mode as well as abipolar mode and a monopolar mode including multiple functions withinthe monopolar mode such as a monopolar cutting function, a monopolarcoagulation function.

In the monopolar cutting function, monopolar RF energy is provided tothe device 30 at a first power level and/or a first waveform(collectively first, or cutting RF energy setting). For example, cuttingRF energy for a cut function may be provided at a relatively low voltageand a continuous current (100% on, or 100% duty cycle). Nominalimpedance can range between 300 to 1000 ohms for the cutting function.At a power setting of 90 Watts for cutting, voltage can range fromapproximately 164 to 300 volts root mean square (RMS).

In the monopolar coagulation function, monopolar RF is energy isprovided to the electrode at a second power level and/or second waveform(collectively second, or coagulating RF energy setting) that isdifferent than at least one of the first power level or the firstwaveform. For example, coagulating RF energy for a coagulation functionmay be provided at a relatively higher voltage than the cut voltage andwith bursts of a pulsed current, such as 1% to 6% on and 99% to 94% off,respectively (or 1% to 6% duty cycle). Other duty cycles arecontemplated.

The electrosurgical unit 10 may provide bipolar RF energy at a thirdpower level and/or third waveform (collectively third, or hemostaticsealing RF energy setting) along with fluid for a (generally lowvoltage) hemostasis or tissue sealing function that may be the same asor different than the cutting and coagulating RF settings provided tothe device 30 for the cut function or the coagulation function. In oneexample, hemostatic sealing energy can be provided with a continuouscurrent (100% duty cycle). Nominal impedance can range between 100 to400 ohms for the hemostatic sealing function. At a power setting of 90Watts for hemostatic sealing, voltage can range from approximately 95 to200 volts RMS.

In one example, the electrosurgical unit 10 provides RF energy to theactive electrode as a signal having a frequency in the range of 100 KHzto 10 MHz. In some cases, this energy is applied in the form of burstsof pulses. In one example, each burst typically has a duration in therange of 10 microseconds to 1 millisecond. The individual pulses in eachburst typically each have a duration of 0.1 to 10 microseconds with aninterval between pulses of 0.1 to 10 microseconds. The actual pulses areoften sinusoidal and bi-phasic, that is alternating positive andnegative amplitudes. Several other features are described in U.S. Pat.No. 8,323,276, to Palanker et al., and incorporated by reference hereinin its entirety to the extent it is not inconsistent with the presentdisclosure.

The electrical surgical unit 10 includes a power switch to turn the uniton and off and an RF power setting display to display the RF powersupplied to the electrosurgical device 30. The power setting display candisplay the RF power setting numerically in a selected unit such aswatts.

The example electrosurgical unit 10 includes an RF power selectorcomprising RF power setting switches that are used to select or adjustthe RF power setting. A user can push one power setting switch toincrease the RF power setting and push the other power setting switch todecrease the RF power setting. In one example, power setting switchesare membrane switches, soft keys, or as part of a touchscreen. Inanother example, the electrosurgical unit may include more than onepower selectors such as a power selector for monopolar power selectionand a power selector for bipolar power selection. The electrosurgicalunit can also include an RF power activation display having an indicatorlight that can illuminate when the RF power is activated either via ahand switch on the device 30, a foot switch, or other switch.

The example electrosurgical unit 10 can also include fluid flow ratesetting display and flow rate setting selector. The display can includeindicator lights, and the flow rate selector can include switches.Pushing one of the flow rate switches selects a fluid flow rate, whichis than indicated in display.

While not being bound to a particular theory, the relationship betweenthe variables of fluid flow rate Q (such as in units of cubiccentimeters per minute (cc/min)) and RF power setting Ps (such as inunits of watts) can be configured to inhibit undesired effects such astissue desiccation, electrode sticking, smoke production, charformation, and other effects while not providing a fluid flow rate Q ata corresponding RF power setting Ps not so great as to disperse too muchelectricity and or overly cool the tissue at the electrode/tissueinterface. Electrosurgical unit 10 is configured to increase the fluidflow rate Q generally linearly with an increasing RF power setting Psfor each of the three fluid flow rate settings of low, medium, and high.

Electrosurgical unit 10 can be configured to include control of the pump22. In this example, the speed of the pump 22, and the fluid throughput,can be predetermined based on input variables such as the RF powersetting and the fluid flow rate setting. In one example, the pump 22 canbe integrated with the electrosurgical unit 10.

Several electrosurgical units, or generators, are described, forexample, in U.S. patent application Ser. No. 14/927,999 to Smith, etal., titled RF Output Stage Switching Mechanism, filed Oct. 30, 2015;U.S. patent application Ser. No. 14/928,020 to Hubelbank, et al., titledFinger Switch Circuitry to Reduce Leakage Current, filed Oct. 30, 2015;U.S. patent application Ser. No. 14/927,969 to Smith, et al., titledPower Monitoring Circuitry and Method for Reducing Leakage Current in RFGenerators, filed Oct. 30, 2015; and U.S. Patent Application PublicationNo. 2006/0149225 to McClurken, each assigned to the assignee of thepresent disclosure and incorporated by reference herein in theirentireties to the extent they are not inconsistent with the presentdisclosure.

While electrosurgical device 30 and surgical retractor 40 are describedwith reference to electrosurgical unit 10 and other elements of system50, it should understood the description of the combination is for thepurposes of illustrating system 50. It may be possible to use theelectrosurgical unit 10 and surgical retractor 40 in other systemsincluding different electrosurgical devices.

FIG. 2 illustrates the system 50 including the electrosurgical unit 10coupled to the electrosurgical device 30 and the surgical retractor 40.The electrosurgical unit 10 includes one or more active electrode outputconnections 26 that is configured to be electrically coupled to theelectrosurgical device 30, such as an electrosurgical device configuredin a monopolar mode, and one or more return electrode receptacles 28,one of which is configured to be coupled to the surgical retractor 40.The example electrosurgical unit 10 can include a controller 60, a highvoltage power supply 62, and an RF output circuit 64. The power supply62 provides high voltage power to the RF output circuit 64, whichconverts high voltage power, for example from a direct current, into RFenergy and delivers the RF energy to an active electrode outputconnection 26. The RF output circuit 64 is configured to generate aplurality of waveforms having various duty cycles, peak voltages, crestfactors, and other suitable parameters.

The controller 60 in the example can include a processor 70 operablyconnected to a memory device 72. Examples of a memory device 72 caninclude a non-volatile memory device such as a read only memory (ROM),electronically programmable read only memory (EPROM), flash memory,non-volatile random access memory (NRAM) or other memory device, and avolatile memory device such as random access memory (RAM) or othermemory device. Memory device 72 can include various combinations of oneor both of non-volatile memory devices and volatile memory devices. Themicroprocessor 70 includes an output port that is operably connected tothe power supply 62, the RF output circuit 64, or both that allows theprocessor 70 to control the output of the electrosurgical unit 10according to a selected scheme. In some examples, the processor 70 maybe substituted with a logic processor or other control circuit.

Any combination of hardware and programming may be used to implement thefunctionalities of the electrosurgical unit 10. Such combinations ofhardware and programming may be implemented in a number of differentways. For example, the programming for the electrosurgical unit 10 maybe processor executable instructions stored on at least onenon-transitory machine-readable storage medium, such as memory device 72and the hardware may include at least one processing resource, such asmicroprocessor 70, to execute those instructions. In some examples, thehardware may also include other electronic circuitry to at leastpartially implement at least one feature of electrosurgical unit 10. Insome examples, the at least one machine-readable storage medium, such asa memory device 72, may store instructions that, when executed by theprocessor 70, at least partially implement some or all features ofelectrosurgical unit 10 and. In such examples, electrosurgical unit 10may include the at least one machine-readable storage medium storing theinstructions and the at least one processing resource to execute amethod. In other examples, the functionalities of electrosurgical unit10 and method may be at least partially implemented in the form ofelectronic circuitry.

The electrosurgical unit 10 also includes a detection circuit 80electrically coupled to the return receptacle 28 and operably coupled tothe controller 60. The features and functions described below asincluded in the detection circuits such as detection circuit 80, in thisdisclosure may be, in some examples, included in or performed with thecontroller 60, vice versa, or some other combination. Furthermore,features and functionality of the detection circuits, such as detectioncircuit 80, can be implemented from one or more of conductors, circuitelements, hardware, and software.

In the example, the detection circuit 80 is able to detect at least thevoltage V_(s) at the surgical retractor 40, which is provided to thereturn electrode receptacle 28 and can also be configured to detect thecurrent i_(s) in the conductor 82 from the surgical retractor 40 to thereturn electrode receptacle 28. The controller 60 also receives a signalindicating at least one of voltage V_(a) at the active electrode 84 andthe current i_(a) provided from the output receptacle 26 in conductor 86to the active electrode 84. The detection circuit 80 and controller 60operate together to determine the impedance over time in the tissueforming an electrical path between the active electrode 84 and thesurgical retractor 40 while treating tissue during surgery. For example,controller 60 can receive a signal representative of the difference involtage between the active electrode 84 and the surgical retractor 40and divide this difference by the measured current from the surgicalretractor 40 to calculate the electrical impedance of the tissue in theelectrical path between the active electrode 84 and the surgicalretractor 40. In some examples, such as if the electrosurgical unitreceives a single return signal from the patient, the current providedto the active electrode 84 from the electrosurgical unit 10, i_(a), isthe same, or about the same less some leakage current, as the currentfrom the surgical retractor 40 provided to the electrosurgical unit 10,i_(s). The calculation of impedance Z_(s) in the tissue between theactive electrode 84 and the surgical retractor 40 at a given time isgenerally determined by Z_(s)=(V_(a)−V_(s))/i_(s).

In one example, controller 60 can include features to present theimpedance measurement over time as a visualization to a display orscreen. In another example, the controller 60 can include an indicatordevice to provide an audio indication or visual indication, such as analarm sound or lights, upon a selected condition of the impedancemeasurement. The impedance measurement indicative of a selectedcondition, in one example, can be related to tissue viability of in thesurgical area adjacent to the surgical retractor 40. Other selectedconditions of interest may be detected via the impedance measurement. Aclinician can receive an indication that an impedance thresholdrepresentative of the selected condition has been reached, andselectively adjust the RF energy to the active electrode 84, i.e., suchas reduce or cut power, or take other action accordingly. Still further,the controller 60 can include a component to automatically adjust poweror signals to the active electrode 84 of the electrosurgical device upondetection of a selected condition via the impedance measurement.

FIG. 3 illustrates a system 50 a including an electrosurgical unit 10coupled to the electrosurgical device 30 and the surgical retractor 40.The electrosurgical unit includes one or more active electrode outputconnections 26 that is configured to be electrically coupled to theelectrosurgical device 30 and a plurality of return electrodereceptacles, such as return electrode receptacles 28 a, 28 b. The firstreturn electrode receptacle 28 a is electrically coupled to the surgicalretractor 40. The second return electrode receptacle 28 b iselectrically coupled to a return pad dispersive electrode 42, in theexample. The second return receptacle 28 b can also be electricallycoupled to a return electrode on a bipolar electrosurgical device. Stillfurther, the electrosurgical unit may include at least three returnelectrode receptacles, one of which is coupled to the surgical retractor40, another of which is coupled to the return electrode on a bipolardevice, and still another of which is coupled to the a return paddispersive electrode 42. Other configurations of multiple returnreceptacles 28 are contemplated.

The example electrosurgical unit 10 a can also include a controller 60,a high voltage power supply 62, and an RF output circuit 64. The powersupply 62 provides high voltage power to the RF output circuit 64, whichconverts high voltage power, for example from a direct current, into RFenergy and delivers the RF energy to an active electrode outputconnection 26. The RF output circuit 64 is configured to generate aplurality of waveforms having various duty cycles, peak voltages, crestfactors, and other suitable parameters. The return receptacles 28 a, 28b are electrically coupled to a detection circuit 80 a, which is alsooperably coupled to the controller 60.

In the example, the detection circuit 80 a is able to detect at leastthe voltage V_(s) at the surgical retractor 40, which is provided to thereturn electrode receptacle 28 a and can also be configured to detectthe current i_(s) in the conductor 82 from the surgical retractor 40 tothe return electrode receptacle 28 a. The controller 60 also receives asignal indicating at least one of voltage V_(a) at the active electrode84 and the current i_(a) provided from the output receptacle 26 inconductor 86 to the active electrode 84. The detection circuit 80 a andcontroller 60 operate together to determine the impedance over time inthe tissue forming an electrical path between the active electrode 84and the surgical retractor 40 while treating tissue during surgery. Forexample, controller 60 can receive a signal representative of thedifference in voltage between the active electrode 84 and the surgicalretractor 40 and divide this difference by the measured current from thesurgical retractor 40 to calculate the electrical impedance of thetissue in the electrical path between the active electrode 84 and thesurgical retractor 40. In some examples, such as if the electrosurgicalunit receives multiple return signals from the patient, the currentprovided to the active electrode 84 from the electrosurgical unit 10,i_(a), is not the same as the current from the surgical retractor 40provided to the electrosurgical unit 10, i_(s). The calculation ofimpedance Z_(r) in the tissue between the active electrode 84 and thesurgical retractor 40 at a given time is determined byZ_(r)=(V_(a)−V_(s))/i_(s).

In some examples, multiple return pads can be included on the surgicalretractor 40. Each of these return pads can provide an electrical signalto the electrosurgical unit 10. The electrosurgical unit 10 can analyzeeach of these signals for relative changes between the signals todetermine whether tissue proximate one return pad includes a change inelectrical characteristics compared to tissue proximate another returnpad. For example, the detection circuit 80 a is able to detect at leastthe voltage V_(s1), V_(s2), V_(sn), in each of the return pads n of thesurgical retractor 40, which is provided to the return electrodereceptacles and can also be configured to detect the current i_(s1),i_(s2), . . . i_(sn), each of the conductors coupled to the n returnpads n of the surgical retractor 40 to the return electrode receptacle28 a. The controller 60 also receives a signal indicating at least oneof voltage V_(a) at the active electrode 84 and the current i_(a)provided from the output receptacle 26 in conductor 86 to the activeelectrode 84. The detection circuit 80 a and controller 60 operatetogether to determine the impedance or impedance over time in the tissueforming an electrical path between the active electrode 84 and the nreturn pads surgical retractor 40 while treating tissue during surgeryand can compare the electrical characteristics to each other to monitorchanges or anomalies.

The detection circuit 80 a and controller 60 can operate together todetermine the impedance or impedance over time in tissue forming anelectrical path between the n return pads on the surgical retractor 40,such as two or more return pads on the surgical retractor 40 in themanner similar to a split pad. For example, an electrical signal at aninterrogation frequency is provided to return pads on the surgicalretractor 40 to measure the impedances in the tissue between the returnpads on the surgical retractor 40. In one example, the interrogationfrequency can be in the range of 1 kHz to 100 kHz and can be providedeven while the electrosurgical device 30 is not activated to monitorimpedance in the tissue between the return pads without application ofthe electrosurgical device 30.

The controller 60 can also receive a signal representative of thedifference in voltage between the active electrode 84 and the return paddispersive electrode 42 and divide this difference by the measuredcurrent from the surgical retractor 40 to calculate the electricalimpedance of the tissue in the electrical path between the activeelectrode 84 and the return pad dispersive electrode 42. In the example,the detection circuit 80 a is able to detect at least the voltage V_(r)at the return pad dispersive electrode 42, which is provided to thereturn electrode receptacle 28 b and can also be configured to detectthe current i_(r) in the conductor 88 from the return pad dispersiveelectrode 42 to the return electrode receptacle 28 b. The calculation ofimpedance in the tissue between the active electrode 84 and the returnpad dispersive electrode 42 at a given time is determined by(V_(a)−V_(r))/i_(r). This impedance measurement can be compared to theimpedance measurement in the tissue between the active electrode 84 andthe surgical retractor 40 for further insight into the condition of thetissue adjacent to the surgical retractor 40.

The detection circuit 80, 80 a in on example may include returnelectrode monitoring circuitry to monitor contact area between thepatient and one or more return pad dispersive electrode 42. Thecircuitry prevents tissue damage caused by pad burns due to poor padcontact. The return electrode monitoring circuitry forms a resonantsystem with split electrode pads of the return pad dispersive electrode42 that are designed to resonate at a specific interrogation frequency.The return electrode monitoring circuitry detects a signal in responseto a supplied drive signal at a predetermined clock frequency (e.g.,from the controller 60). The return electrode monitoring circuitryproduces a voltage indicative of the amplitude (e.g., magnitude) of thewaveform indicative of the resonations. As the impedance between thesplit pads changes, the resonance of the return electrode monitoringcircuitry changes as well, which causes the amplitude to change. Thus,by monitoring the changes in the amplitude, the return electrodemonitoring circuit determines the magnitude of the impedance between thesplit pads, which is indicative of adherence of the return paddispersive electrode 42 to the patient. In one example, surgicalretractor 40 can be configured to include split return pads, and thereturn electrode monitoring circuitry can be applied to detect aselected amount of contact between the tissue at the surgical site andsplit return pads on the surgical retractor 40.

FIG. 4 illustrates a surgical retractor 100 that allows a user tomanipulate and tissues of a patient and is an example of surgicalretractor 40. The manipulation, for example, may be expansion orretraction of skin, muscle, organs, bone or other tissues. In oneexample, the surgical retractor 100 may be used to perform surgery onthe breast, such as gynecomastia correction, augmentation, mastopexy,reduction, and skin sparing or nipple sparing mastectomies prior tobreast reconstruction. The surgical retractor 100 allows for aconservative sized incision for introduction, removal, or replacement ofa breast implant. It also facilitates visualization for effectivehemostasis in a breast pocket and dissection of the periphery of thebreast pocket. Still further, the surgical retractor provides an abilityto gauge the viability of breast flap tissue or other tissue at thesurgical site using electrosurgical signals that travel through thetissue from the electrosurgical device to the surgical retractor.Additionally, the surgical instrument 100 may be used to perform surgeryon a patient's abdomen, pelvis, or trunk and limbs, such as dissectionof a pedicled or free flap, like a latissimus dorsi muscle forreconstruction as well as to gauge the viability of such tissue incontact with the surgical retractor 100.

The surgical retractor 100 has a handle 102, a blade 104, and a returnelectrode 106. In the example, the surgical retractor 100 can alsoincludes a light 110 disposed on the blade 104, a power source 112(shown in phantom) disposed within the surgical retractor 100, such asthe within the handle 102, and a light switch 114 disposed on the handle102.

The handle 102 and the blade 104 may be made of a rigid, sterilizable,electrically insulative material such as a synthetic polymer. Thesynthetic polymer can include polycarbonate,acrylonitrile-butadiene-styrene, or other suitable materials.Lightweight materials also permit a clinician to use the device overlong periods of time with less fatigue. In one example, the surgicalretractor 100 is composed of materials permitting it to be readily andeconomically disposable.

The handle 102 includes a proximal end 120, a base end 122, and anintermediate portion 124. The handle 102 a can be configured to behand-held and may have a grip handle, a cylindrical grip, or otherergonomic design to be held by a user. In some examples, the handle 102has protrusions such as vertical or horizontal ridges, to facilitatecomfortable or ergonomic holding by the user. The handle 102 can includea flared top 126 near the proximal end 120 to allow the handle 102 to bemore easily gripped and held. The handle 102 may be made of a soft, foamplastic material to provide a comfortable, resilient grip. In someexamples, the handle 102 is shaped to permit connection to a clamp, aholding mechanism, or other device to mount the surgical retractor 100to a surgical table or to a floor stand.

The blade 104 extends from the base end 122 of the handle 102 and may begenerally flat and generally rectangular in profile. Other bladeprofiles or crosssections sufficient to manipulate the patient's tissuesmay be used, such as cylindrical, paddle-shaped, rectangular, orconical. In some examples, at least a portion of the length of the blade104 is generally oblique to the handle 102. In the depicted embodiments,the blade 104 can be generally perpendicular to the handle 102. Theblade 104 could also be at any angle to the handle 102. In someexamples, the angle of blade 104 may be adjustable with respect to thehandle 102, such as by inclusion of a hinge in the blade or at theattachment point of the blade with the handle 102, such as at the baseend 122. In some examples, the blade 104 may be detachable from andattachable to the handle 102, such as by inclusion of an attachmentmechanism in the blade 104 or the handle 102. For example, a user maydetach a first blade of a selected first configuration from the handleand attached a second blade having a selected second configuration tothe handle. Alternatively, a user may detach a first handle of aselected first configuration from the blade and attached a second handlehaving a selected second configuration to the blade.

The blade 104 includes a first major surface 130, which is configured tointerface with tissue during surgery, and an opposite, second majorsurface 132. The blade 104 can include a base 134 and tip 136. The blade104 can include first and second side edges 138, 140, and a tip edge142. The width of the blade 104 can be described as the distance betweenthe first and second side edges 138, 140, and the length of the bladecan be described as the distance between the base 134 and the tip 136.

In some examples, the blade 104 includes a flared tip (not shown), wherethe tip is oblique to the adjacent portion of the blade 104. Such aflared tip can facilitate movement of the tip among the patient'stissues. In some examples, the blade 104 has tines, or teeth (notshown), at the tip 136 to grip or maneuver the tissues. In someexamples, the blade is extendable or adjustable (not shown). Forexample, the length or width of the blade may be made longer or shorter,for example, by sliding one portion of the blade relative to anotherportion.

The blade 104 includes a base portion 146 formed of the rigid,sterilizable, electrically insulative material such as the syntheticpolymer forming the first major surface 130 and the second major surface132. A return electrode 106 is affixed to the base portion 146 such ason the first major surface 130. The return electrode 1 is formed fromelectrically conductive material such as metal and may comprisestainless steel, titanium, gold, silver, platinum or any other suitablematerial. The configuration of the return electrode 106 can vary. Forexample, the return electrode 106 may be formed as a pad conductorhaving a rectangular profile or some other geometry, may be a narrowconductor strip extending along the length of the blade 104, may be agrid of narrow conductors in a mesh-like arrangement, or some othersuitable configuration. The return electrode 106 may be a single foilconfiguration or a split foil configuration and may include one or moresingle foil or split foil return electrodes. In some examples, a returnelectrode may be attached to the second major surface 134 in addition toor instead of the first major surface 132. In the case of electrodesdisposed on both the first and second major surfaces 132, 134, theelectrodes may be electrically coupled to each other or electricallyisolated from each other on the blade 104.

The return electrode 106 is electrically coupled to one or moreelectrical conductors that can be disposed on or within the surgicalretractor 100 such as within the handle 102. Multiple electricalpathways are electrically coupled to the return electrode 106 in thecase of a slit foil configuration, multiple return electrodes, or otherconfiguration. In the case of a multiple conductors such as split foilpad, the current to each of the foils could be differentiated to measurerelative conductivity of the tissue above both foils in relation to eachother. Electrical pathways within the handle 102 can be formed asconductive arms, wires, traces, other conductive elements, and otherelectrical pathways formed from electrically conductive material such asmetal and may comprise stainless steel, titanium, gold, silver, platinumor any other suitable material. The electrical pathways can extend fromthe handle 102 via cable 148 at proximal end 120. In one example, cable148 can include one or more connectors (not shown) that can beelectrically and mechanically coupled to the proximal end 120 and to anelectrosurgical unit, such as electrosurgical unit 10. Cable 148 cancorrespond with cable 32 and include one or more conductors, such asconductor 82, as electrical pathways.

The light 110 can be used to illuminate the tissues adjacent to orproximate the blades such as the surgical cavity. The light 110 maylocated at the base end 122 of the handle 102, on the blade 104, such ason the second major surface 134, or elsewhere on the surgical retractor100. The light 110 can include one or more light emitting diodes (LEDs)that may be enclosed in a translucent, including transparent, covering.The light 110 may include electrical or thermal insulation.

The power source 112 may be disposed within the handle 102 and mayinclude at least one battery or other energy storage element to provideenough power to last through surgery. A battery life of four to fivehours may be sufficient. In some examples, the power source 112 isremovable so that it may be recharged.

In addition, the surgical retractor 100 may include a light switch 114to selectively electrically couple the power source 112 to the light110. In one example, the light switch may be a push button or toggleswitch disposed on the handle 102 near the location of a clinician'sthumb or forefinger for easy accessibility. In some examples, the lightswitch 114 may be used to select one of a plurality of levels ofillumination from the light 110. The light switch 114 may include aswitch guard formed into the handle 102 to reduce the likelihood thatthe light 110 is inadvertently activated or deactivated.

The surgical retractor 100 may include additional features orfunctionalities. For example, the handle 102 or blade 104 may have achannel or tube that can be connected to a suction device, such as asuction tap in an operating room, to provide aspiration of gas or fluidfrom the surgical region or surgical cavity. Additionally, the surgicalretractor can include a camera or be configured to accept a camera. Inone example, the camera includes a wireless transmitter that can belocated within the handle 102.

FIG. 5 illustrates another surgical retractor 100 a having a blade 104detachable from the handle 102. The blade 104 includes a returnelectrode 106 attached to the first major surface 130. The surgicalretractor 100 a can include features and functionality of surgicalretractor 100. For example, the surgical retractor 100 a can alsoinclude a blade 104 having a light 110 disposed on the second majorsurface 132. A power source 112 can be disposed within the handle 102,and a light switch 114 disposed on the handle. The surgical retractor100 a further includes a mechanical coupling 150 proximate the base end122 of the handle 102 and the base 134 of the blade such that the baseend 122 of the handle 102 can be selectively coupled to or decoupledfrom the base of the blade 104. Additionally, the mechanical coupling150 can include one or more electrical couplings, such as a detachableelectrical connection to selectively electrically connect the returnelectrode 106 to an electrical pathway in the cable 148 in cases whenthe blade 102 is mechanically coupled to the handle 102. In the case ofthe surgical retractor 100 a including light 110, the mechanicalcoupling can also include a detachable electrical connection toselectively electrically connect the light 110 to the power source 112in cases when the blade 102 is mechanically coupled to the handle 102.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. An electrosurgical unit, comprising: an RF outputconfigured to be coupled to an electrosurgical device; an RF returnconfigured to be coupled to a surgical retractor; and a controlleroperably coupled to the RF output and the RF return, the controllerconfigured to determine an impedance in tissue at a surgical areaelectrically disposed between the RF output and the and the RF return.2. The electrosurgical unit of claim 1 comprising a detection circuitoperably coupled to the RF return and the controller.
 3. Theelectrosurgical unit of claim 2 wherein the detection circuit includes areturn electrode monitoring circuit.
 4. The electrosurgical unit ofclaim 1 wherein the controller includes a processor and memory device.5. The electrosurgical unit of claim 1 comprising a RF circuit operablycoupled to the controller and the RF output.
 6. The electrosurgical unitof claim 1 wherein the controller is configured to output the determinedimpedance.
 7. The electrosurgical unit of claim 6 wherein the outputincludes a visualization.
 8. The electrosurgical unit of claim 1 whereinthe determined impedance includes calculating the difference between avoltage at the RF output and a voltage at the RF return dived by acurrent received at the RF return.
 9. The electrosurgical unit of claim1 comprising a plurality of RF returns.
 10. An electrosurgical unit,comprising: an RF output configured to be coupled to an electrosurgicaldevice; a first RF return configured to be coupled to one of theelectrosurgical device and a return pad dispersive electrode; a secondRF return configured to be coupled to a surgical retractor; and acontroller configured to determine an impedance in tissue at a surgicalarea electrically disposed between the RF output and the second RFreturn, and the controller configured to determine an impedance
 11. Theelectrosurgical unit of claim 10 wherein the determined impedanceincludes calculating the difference between a voltage at the RF outputand a voltage at the second RF return dived by a current received at thesecond RF return.
 12. The electrosurgical unit of claim 11 wherein thecontroller is configured to determined a return electrode impedance fromcalculating the difference between a voltage at the RF output and avoltage at the first RF return dived by a current received at the firstRF return.